Before you ever see the first shot of “Youth in Revolt,” you know what’s going on. A repetitive motion sound can be heard as well as the flipping of pages. Nick Twisp (Cera) is masturbating and almost everyone in the theater knows it. That’s testament to how far the R-rated comedy sexual revolution has come over the last decade, so it’s not surprising to see a film so unabashed about teenage sex let alone one whose entire plot is driven by a teenagers zealous appetite to shed his virginity.

The always soft-spoken and awkwardly verbose Cera plays yet another character that fits his mold in Twisp, a teenager with divorced parents who loves Fellini films and vintage vinyl and really, really wants to get laid. It’s a semi-romantic aspiration as well, but the depths to which he’ll let his hormones take him is at times even implausibly absurd.

On vacation with his mother (Jean Smart) and her lover Jerry (Zach Galifianakis of “The Hangover”), Nick meets a perfect match in the daughter of two devout Christian trailer park folks named Sheeni Saunders and the two have an awkward but adorable summer fling. Newcomer Portia Doubleday makes an impression in this early portion of the film as Sheeni, teasing Nick and viewers with her poise and charm. When Nick has to go, he realizes their relationship (and his ascent to manhood) is at risk. He devises a scheme to get his father to move to Sheeni’s town and his mother to get mad enough to send him to live there. The only problem, is that for it to work, sweet and innocent Nicky will have to be bad.

Nick invents an alternate persona for himself, one based on Sheeni’s ideal man. He’s a blue- eyed mustached, chain-smoking Frenchman named Francois Dillinger and he’s Nick without hesitation or reservation. Cera does wisely in agreeing to be in this film because of this alter- ego aspect. Having to be Francois pushes Cera out of that same old wimpy character box and has him being frank — and really dirty — for once. If Cera doesn’t want to flame out in the near future, he’ll need more parts like this.

From here on out, “Youth in Revolt” sort of tumbles into a teenage daydream of all the insane things any good, normal kid would do for love and sex — if it were all fiction. The creation of Francois doesn’t exactly justify the ridiculous decisions Nick makes like burning down half of Berkeley, California, for example. It’s fun, but not all that memorable.

I’ve never read the C.D. Payne novel, but you can tell it was much more extensive and that Gustin Nash had a hard time with the adaptation. All the events feel compressed, especially in the middle and last acts. Nothing builds gradually, it just gets stuck in. Some characters such as Sheeni’s drug-endorsing older brother (Justin Long) who’s snuck in toward the end, feel important to the story in an intangible way, but don’t leave any particular impression.

Nash’s adaptation, despite having the comedic dialog down, lacks a clear interpretation of Payne’s story by which to tailor itself. In other words, deciding on one of the book’s messages to craft the adaptation around might’ve helped eliminate certain parts of the story and alleviate the cramming. Director Miguel Arteta picks up on some subtler ideas such as how the many side characters act as insight on or inspire rebellious behavior, but they mostly get lost in the love story and Nick’s sexual coming-of-age.

“Youth In Revolt” is an explicit teenage Rated-R comedy, but not a raunchy one, which ultimately makes it more respectable than more than half the genre off-the-bat. Much respect to The Weinstein Co. and Dimension Films for not trying to taper back for a PG-13 considering R closes the film off to half its intended audience. At the same time, it’s not as unique or genre-changing as Areta’s indie stylings try and make it out to be. Once again, audiences have grown accustomed to an assortment of male genital references and open discussion about sex. But there are some good performances from young actors and clever dialog in “Youth in Revolt” and it deserves a viewing.